PWM Controller Based on 555 Timer

Overview

The project aims to create a PWM controller that contains a frequency range from about 170 to 200Hz to achieve a pulse width regulation featuring almost 0-100% with a relatively stable oscillator frequency.

Details

The frequency range provided by the device depends on the values of R1 and C1 from the schematic diagram. Although a CMOS can be used in the design, a 555 chip was chosen along with a 1N4148 diode. The 555 timer is kept in reset state for about 2 seconds by a kickstart circuit comprised of R2, R3, and C3. The PWM cycle is driven by the Q output of 555 which makes the output transistor to be driven using the discharge pin. This allows the kickstarter to work as the open collector output is used as active low signal.

The 3-wire fan is driven using the connectors while feeding the tachometer output to motherboard. Whenever the PWM cycle removes power from fan, a normal tachometer output also disappears. An 80mm power supply fan can be handled by this controller. A thermistor can be used between wiper to make it more high-tech by making the PWM cycle temperature dependent.

Rest of the project